A reference signal (RS) may be classified as a wireless transmit/receive unit (WTRU)-specific reference (WTRU-RS) and a cell-specific reference signaling (CRS). The WTRU-RS may be used on for a specific WTRU so that the RS is transmitted for the resources allocated to the WTRU. On the other hand, the CRS may be shared by all WTRUs in a cell so that the RS is transmitted in a wideband manner. In addition, according to the usage of the RS, it may be further differentiated to at least one of a demodulation reference signal (DM-RS) and a channel-state-information reference signal (CSI-RS).
The DM-RS may be used only for a specific WTRU and the RS is typically precoded to exploit beamforming gain. The CRS may be defined for all WTRUs in a cell and may be used for demodulation and measurement purposes.